1. Field of the Invention
This invention relates generally to mooring systems for offshore structures such as platforms and vessels and in particular, to a device which supports the mooring chain in such systems.
2. Description of the Prior Art
Offshore structures such as platforms (e.g. tension leg and SPAR platforms) and vessels (e.g., floating storage and offloading vessels; floating production storage and offloading vessels; and floating storage drilling production and drilling units) at times, require a moored (or anchored) connection to the sea floor. Such moored connections enable the offshore structure to remain in a relatively stable position resisting forces caused by environmental conditions such as wind, waves, and the like. To establish the moored connection, an anchor is embedded into the seafloor, and a mooring chain or the like is attached thereto. The moored chain is then attached to a guideline from the offshore structure and xe2x80x9creeledxe2x80x9d in until a desired tension is created on the chain between the buoyant uplift of the offshore structure and downward pulling force of the anchor. To facilitate this reeling, a plurality of different chain guides and devices are known in the art. To maintain the tensile connection, a chain stopper or device is needed.
U.S. Pat. No. 5,845,893, issued to Groves discloses two devices for maintaining tension. The first, xe2x80x9ca latch mechanism,xe2x80x9d includes a latch housing and bending shoe, which are gimbaled to the offshore structure. The chain is passed through the latch housing; and then, when a desired tension is reached, a latch engages the chain via a manual intervention or a remotely operated hydraulic device. The second, xe2x80x9ca pelican hook,xe2x80x9d works in a similar manner, but engages the chain via a book using a hydraulically actuated arm.
A primary object of the invention is to provide a simple and inexpensive chain support that requires no powered actuator for latching the chain.
Another object of the invention is to provide a chain support with minimal moving parts.
Another object of the invention is to provide a chain support that provides a latching mechanism with no moving parts.
Another object of the invention is to provide a chain support assembly that has only one moving part, no manually manipulated chain stopper, using readily available materials at a cost lower than designs currently used.
The objects identified above along with other advantages and features are incorporated in a chain support that latches a mooring chain without an actuator required The swing arm with a hook fixed thereto, is mounted so that it can pivot about a horizontal axis with respect to the offshore structure. The swing arm has a mouth in which two plates are mounted parallel to each other to form a passage between each other that is separated by a distance large enough to allow a guideline to pass, but small enough to prevent a guide device or a perpendicularly oriented chain link from passing through. Chain links which are oriented parallel to the passage pass through the passage while the chain is being pulled up through the swing arm. Chain links oriented perpendicularly to the passage are too wide to pass through the passage. The plates include sloping guide ramps which are arranged so that when a perpendicular oriented chain link passes through the mouth and meets the ramps through upward pulling tension, the force of the perpendicular chain link causes the swing arm to pivot upwardly. The swing arm pivots upwardly and downwardly for ratcheting of the chain links when they are pulled altematingly through the passage between the plates and over the ramps of the plates. When tension is relaxed on the chain, the swing arm rotates downwardly and a link is captured by the hooks of the plates.